Electromagnetic ultrasonic double-wave transducer

ABSTRACT

An electromagnetic ultrasonic double wave transducer, comprising a shell (1), and a permanent magnet assembly, a coil (4), a shielding layer (5), and a wire (6) which are provided in the shell (1). The permanent magnet assembly comprises a first permanent magnet (2) and a second permanent magnet (3) sleeved on the first permanent magnet (2). The magnetizing directions of the first permanent magnet (2) and the second permanent magnet (3) are perpendicular to the bottom of the shell (1), and the magnetic field directions of the first permanent magnet (2) and the second permanent magnet (3) are opposite. A non-conducting non-magnetic bushing material (9) is provided between the first permanent magnet (2) and the second permanent magnet (3), and upper end faces of the first permanent magnet (2) and the second permanent magnet (3) realize magnetic circuit closing by means of a magnetic circuit closing element (8). The coil (4) is fixed on the bottom of the shell (1) and is located below the first permanent magnet (2). The shielding layer (5) is provided between the lower end of the first permanent magnet (2) and the coil (4) and below the second permanent magnet (3). One end of the wire (6) is connected to the coil (4), and the other end is connected to the power supply and signal plug (7). The electromagnetic ultrasonic double-wave transducer can simultaneously stimulate longitudinal wave and transverse wave on the surface of the part to be inspected, and the inspection accuracy is improved.

FIELD OF THE INVENTION

The invention relates to the technical field of ultrasonic inspection,specifically relating to an electromagnetic ultrasonic double-wavetransducer.

BACKGROUND OF THE INVENTION

In the field of ultrasonic inspection, it is sometimes necessary to usetwo modes of waves to accurately detect a part for inspection forcertain material properties, dimensions, or defects. For example, in thedetection of the nodularity of spheroidal graphite cast iron, if thereis only one mode of waves, it is not easy to distinguish whether thechange in the time-of-flight is from a change in the thickness of thesample or from a change in the speed of the ultrasonic wave itself,which greatly affects the effectiveness of the inspection. For example,in the assessment of the tensile force of the bolt, if only one mode ofultrasonic wave is adopted, it cannot be known whether thetime-of-flight of the ultrasonic wave is from the change of the part'sdimension or the change of the speed of the ultrasonic wave caused bythe tensile stress of the bolt. Thus, the bolt tension cannot bedetected by an ultrasonic method.

In order to generate ultrasonic waves of two different modes, the openliterature 1 (NDT&E International42(2009)164-169) mentioned that theultrasonic longitudinal wave generates mode-converted transverse wave onthe reflection bottom surface of the part to be measured by employing aspecially designed piezoelectric ultrasonic transducer; the openliterature 2 (Ultrasonics 54(2014)914-920) mentions that anelectromagnetic ultrasonic transverse wave transducer generatesmode-converted longitudinal wave at the reflection bottom of the part tobe tested by using a high-power source for excitation and a multipleaveraging method; the open literature 3 (Vol.17(1996)No.6 662-665,Chinese Journal of Scientific Instrument) mentions that the ultrasoniclongitudinal waves and transverse waves are respectively generated inthe testing part by adopting two piezoelectric transducers incombination; the open literature 4 (U.S. Pat. No. 8,511,165B2) mentionsthe use of a piezoelectric transducer in combination with anelectromagnetic ultrasonic transducer to generate longitudinal andtransverse waves, respectively, on the surface of a testing part.

None of the methods in the above open literature can generate bothlongitudinal wave and transverse wave on the surface of the part to beinspected, causing errors in high-precision inspection, particularly inbolt tension inspection. The piezoelectric transducers referred to inthe open literature 1 to 4 need to take the influence of the wedges andthe couplant on the propagation time of the ultrasonic wave during theforward and backward propagation of the ultrasonic wave from thepiezoelectric wafer to the surface of the part to be tested. Neither ofthe electromagnetic ultrasonic transducers described in the openliterature 2 and 4 can generate ultrasonic longitudinal wave on thesurface of a testing part.

Summary of the invention

Based on the problems in the prior art, the invention aims at providingan electromagnetic ultrasonic double-wave transducer, which cansimultaneously generate longitudinal wave and transverse wave on thesurface of a testing part.

Based on the above problems, the invention provides a technicalsolution:

An electromagnetic ultrasonic double-wave transducer, comprising ashell, and a permanent magnet assembly, a coil, a shielding layer, and awire which are provided in said shell.

Said permanent magnet assembly comprises a first permanent magnet and asecond permanent magnet sleeved on the first permanent magnet. Themagnetizing directions of the first permanent magnet and the secondpermanent magnet are perpendicular to the bottom of said shell, and themagnetic field directions of said first permanent magnet and the secondpermanent magnet are opposite; a non-conducting non-magnetic bushingmaterial is provided between said first permanent magnet and said secondpermanent magnet, and upper end faces of said first permanent magnet andsaid second permanent magnet realize magnetic circuit closing by meansof a magnetic circuit closing element.

Said coil is fixed on the bottom of said shell and is located below saidfirst permanent magnet. Said shielding layer is provided between thelower end of said first permanent magnet and said coil and below saidsecond permanent magnet. One end of said wire is connected to said coil,and the other end is connected to power supply and signal plug.

In one embodiment, said first permanent magnet is cylindrical while saidsecond permanent magnet is annular.

In one embodiment, the inner diameter of said second permanent magnet is1-15 mm larger than the outer diameter of said first permanent magnet.

In one embodiment, the lower end faces of said first permanent magnetand said second permanent magnet have a height difference from −3 mm to3 mm.

In one embodiment, said coil is helical, and the outer diameter thereofis larger than the outer diameter of said first permanent magnet andsmaller than the inner diameter of said second permanent magnet.

In one embodiment, the non-conductive material is filled between saidcoil and said shielding layer, and the non-conducting non-magneticmaterial is filled between said permanent magnet assembly and saidshell.

In one embodiment, said shell includes a shell body and a wear platedisposed at the lower end of said shell body.

Based on the above problems, the second technical solution provided bythe invention is as follows:

An electromagnetic ultrasonic double-wave transducer, comprising ashell, and a permanent magnet assembly, a coil, a shielding layer, and awire which are provided in said shell. Said coil is fixed on the bottomof said shell and is located below said permanent magnet assembly; saidshielding layer is arranged between said permanent magnet assembly andsaid coil; one end of said wire is connected to said coil while theother end thereof is connected to power and signal plug; said permanentmagnet assembly comprises a third permanent magnet and a fourthpermanent magnet wherein the fourth permanent magnet are arranged sideby side with said third permanent magnet and located on two sides of thewidth direction of said third permanent magnet, and said fourthpermanent magnet and said third permanent magnet are arranged atintervals and said intervals are made of non-conducting non-magneticbushing material; the upper end faces of said third permanent magnet andsaid fourth permanent magnet realize magnetic circuit closing by meansof a magnetic circuit closing element.

In one embodiment, the cross sections of said third permanent magnet andsaid fourth permanent magnet are rectangular.

In one embodiment, said coil is butterfly shaped.

In one embodiment, the non-conductive material is filled between saidcoil and said shielding layer, and the non-conductingnon-magnet-conduction material is filled between said permanent magnetassembly and said shell.

In one embodiment, said shell includes a shell body and a wear platedisposed at the lower end of said shell body.

Compared with the prior art, the invention has following advantages;

By adopting the technical solution of the invention, the ultrasonictransducer can simultaneously excite longitudinal waves and transversewaves on the surface of a testing part, and the two modes of ultrasonicwaves are used for detecting physical quantities such as materialproperties like elastic modulus of materials, defects, length, stressand the like, thereby the measurement error caused by the time delay ofthe piezoelectric ultrasonic wedge and the coupling agent is avoided,the detection error possibly caused by the mode conversion of theultrasonic waves is also avoided, and the detection precision isimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of theembodiments of the invention, the drawings required to be used in thedescription of the embodiments are briefly introduced below, thedrawings in the description are only some embodiments of the invention,and it is obvious for those skilled in the art that other drawings canbe obtained according to the drawings without creative efforts.

FIG. 1 is a schematic structural diagram illustrating the embodiment 1of the electromagnetic ultrasonic double-wave transducer in theinvention;

FIG. 2 is a schematic structural diagram of embodiment 2 of theinvention;

FIG. 3 is a sectional view of FIG. 2 along line A-A;

FIG. 4 illustrates that the electromagnetic ultrasonic double-wavetransducer of embodiment 1 simultaneously excites transverse wavesignals and longitudinal wave signals when detecting the Young's modulusand the Poisson's ratio of isotropic materials;

FIG. 5 is an enlarged view illustrating the gain of the electromagneticultrasonic double-wave transducer of embodiment 1 simultaneously excitestransverse wave signals and longitudinal wave signals when detecting theYoung's modulus and the Poisson's ratio of isotropic materials;

FIG. 6 is the longitudinal wave signals and the transverse wave signalsgenerated simultaneously when the electromagnetic ultrasonic double-wavetransducer of embodiment 1 detects tension of a bolt;

FIG. 7 illustrates that time-of-flight ratio of the transverse wavesound to the longitudinal wave sound generated simultaneously when theelectromagnetic ultrasonic double-wave transducer of embodiment 1 isused for bolt tension detection is in one-to-one relationship;

FIG. 8 is an enlarged view illustrating the gain of the electromagneticultrasonic double-wave transducer of embodiment 2 simultaneously excitestransverse wave signals and longitudinal wave signals when detecting theYoung's modulus and the Poisson's ratio of isotropic materials;

Wherein:

1. Shell; 1-1. Shell body; 1-2.Wear plate;

2. The first permanent magnet;

3. The second permanent magnet;

4. Coil;

5. Shielding layer;

6. Wire;

7. Power supply and signal plug;

8. Magnetic circuit closing element;

9. Non-conducting non-magnetic bushing material;

10. Non-conductive material;

11. Non-conducting non-magnetic material;

12. The third permanent magnet;

13. The fourth permanent magnet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The above-described solution is further illustrated below with referenceto specific embodiments. It should be understood that these embodimentsare for illustrative purposes and are not intended to limit the scope ofthe invention. The conditions used in the embodiments may be furtheradjusted according to the conditions of the particular manufacturer, andthe conditions not specified are generally conditions used in routineexperiments.

As is shown in FIG. 1, a schematic structural diagram of the embodimentin the invention provides an electromagnetic ultrasonic double-wavetransducer, comprising a shell 1, and a permanent magnet assembly, acoil 4, a shielding layer 5, and a wire 6 which are provided in theshell 1.

The permanent magnet assembly comprises a first permanent magnet 2 and asecond permanent magnet 3 sleeved on the first permanent magnet 2. Themagnetizing directions of the first permanent magnet 2 and the secondpermanent magnet 3 are perpendicular to the bottom of the shell 1, andthe magnetic field directions of the first permanent magnet 2 and thesecond permanent magnet 3 are opposite. A non-conducting non-magneticbushing material 9 is provided between the first permanent magnet 2 andthe second permanent magnet 3, and upper end faces of the firstpermanent magnet 2 and the second permanent magnet 3 realize magneticcircuit closing by means of a magnetic circuit closing element 8.

Said coil 4 is fixed on the bottom of said shell 1 and is located belowsaid first permanent magnet 2. Said shielding layer 5 is providedbetween the lower end of said first permanent magnet 2 and said coil 4and below said second permanent magnet 3. One end of said wire 6 isconnected to said coil 4, and the other end is connected to a powersupply and signal plug 7.

In this embodiment, the magnetic circuit closing element 8 is made ofmild steel or ferrite with a thickness greater than 3 mm. Thenon-conducting non-magnetic bushing material 9 is made of plastic,rubber or polymer material, such as bakelite.

The inner diameter of said second permanent magnet 3 is 1-15 mm largerthan the outer diameter of said first permanent magnet 2, and said coil4 is helical, and the outer diameter thereof is larger than the outerdiameter of said first permanent magnet 2 and smaller than the innerdiameter of said second permanent magnet 3. The lower end face of thefirst permanent magnet 2 can be flush with that of the second permanentmagnet 3, and they also can have a height difference of less than 3 mm,which means that the lower end face of the first permanent magnet 2 islocated above that of the second permanent magnet 3, or is located belowthat of the second permanent magnet 3.

In this embodiment, the shielding layer 5 is a highly conductive coppersheet or silver sheet, and is attached to the lower ends of the firstpermanent magnet 2 and the second permanent magnet 3.

In order to further optimize the implementation effect of the invention,the non-conductive material 10 is filled between said coil 4 and saidshielding layer 5, such as air, resin and non-conductive soft magneticmaterial; the non-conducting non-magnetic material is filled betweensaid permanent magnet assembly and said shell 1, i.e., epoxy resin.

In this embodiment, said coil 4 is made of double-layer PCB board orwound by enameled wire.

In this embodiment, said shell 1 includes a shell body 1-1 and a wearplate 1-2 disposed at the lower end of said shell body 1-1; the wearplate 1-2 is made of ceramic wafer or epoxy plate and the shell body 1-1is made of stainless steel, aluminum alloy or red copper material; thepower supply and signal plug 7 is fixed at the upper part of the shellbody 1-1.

As is shown in FIGS. 2 and 3, the schematic structural diagram ofembodiment 2 is the same as the embodiment 1 except structure of thepermanent magnet assembly and structure of the coil 4; the permanentmagnet assembly comprises a third permanent magnet 12 and a fourthpermanent magnet 13 wherein the fourth permanent magnet 13 are arrangedside by side with said third permanent magnet 12 and located on twosides of the width direction of said third permanent magnet 12, andbetween said fourth permanent magnet 13 and said third permanent magnet12 are non-conducting non-magnetic bushing material 9;

In this embodiment, the cross sections of said third permanent magnet 12and said fourth permanent magnet 13 are rectangular and said coil 4 isbutterfly shaped.

In the implementation, the first permanent magnet 2, the secondpermanent magnet 3, the third permanent magnet 12 and the fourthpermanent magnet 13 are all made of NdFeB materials.

The electromagnetic ultrasonic transducer can simultaneously excitevertical downward-transmitted ultrasonic transverse waves and ultrasoniclongitudinal waves on the near surface of a conductive or magnetictesting part such as low-carbon steel, aluminum alloy and the like, andthe amplitude of the longitudinal waves excited by said electromagneticultrasonic transducer can reach 20% to 30% of the transverse waves atmost in a test with a matched instrument. While the conventionalelectromagnetic ultrasonic transducer can hardly excite longitudinalwave.

For example, the Young's modulus and the Poisson's ratio of isotropicmaterials were detected by using the electromagnetic ultrasonicdouble-wave transducer of embodiment 1.

In isotropic materials, the elasticity modulus E and Poisson's ratio vare related to the velocity of the longitudinal wave C_(l) and thetransverse wave C_(S) as follows:

$\begin{matrix}{E = \frac{\rho{C_{s}^{2}( {{3T^{2}} - 4} )}}{T^{2} - 1}} & (1) \\{v = \frac{T^{2} - 2}{2( {T^{2} - 1} )}} & (2)\end{matrix}$

where T is defined as T≡C_(l)/C_(S), ρ is the density, and taken7.87×10³ kg/m³ for 20# carbon steel.

Therefore, the Young's modulus and the Poisson's ratio of the materialcan be estimated by detecting the longitudinal wave velocity, thetransverse wave velocity and the density of the material.

A hand-held high-power ultrasonic testing instrument PREMAT-HS200manufactured by Suzhou Phaserise Technology Co., Ltd. is used as anelectromagnetic ultrasonic pulser/receiver equipped with theelectromagnetic ultrasonic double-wave transducer of the invention. Thetesting part is selected from a CSK- II A standard sample according toJB/T 4730-2005 standard. The sample dimension is 300 mm long, 60 mm wideand 40 mm in height The electromagnetic ultrasonic transducer is placedin the middle of the upper surface of the sample to be tested, and is170 mm away from the left edge of the sample, and 35 mm away from theupper edge. The test frequency is 4 MHz, the excitation voltage 1200Vpp, the display delay 10 μs, the sampling time 80 μs, the samplingspeed 100 MS/s, and the repetition rate 200 Hz. The test data for theautomatic gain is shown in FIG. 4. Increasing the gain further on thebasis of FIG. 4 results in FIG. 5. In FIG. 5, multiple periodic echoesand mode-converted waves are labeled, and it can be seen that theelectromagnetic ultrasonic double-wave transducer of the inventionexcites longitudinal waves (first echo is LL) and transverse waves(first echo is SS) simultaneously on the surface of the sample.

Calculations from equations (1) and (2) using the data in table 1 leadto:

E=2.1226×1011 Pa   (3)

v=0.285   (4)

The results are very close to the nominal value of the sample.

TABLE 1 Time-of-flight of longitudinal wave and transverse wave excitedon surface of the testing part. Average wave velocity of transverse LLSS SSSS SSSSSS wave Time (ns) 1354.13 24707 49402 74097 3239.5 m/s Soundvelocity 5907.85 — — — — of longitudinal Waves (m/s)

The transducer of the invention can be used for accurate detection ofbolt tension. According to the open literature 5(Yuping Shen, G. B. Ma,C. Ma, X. X. Zhu and J. H. Zhao, “Bolt stress inspection by EMAT andPZT”,15th Asia Pacific Conference for Non-Destructive Testing,Singapore), the Bolt tension σ can be expressed as

$\begin{matrix}{\sigma = \frac{{TO{F_{S} \cdot C_{S\; 0}}} - {TO{F_{l} \cdot C_{l\; 0}}}}{{{\gamma( {{\partial{+ 1}}/E} )}TO{F_{l} \cdot C_{l0}}} - {{r( {\beta + {1/E}} )}{{TOF}_{S} \cdot C_{S\; 0}}}}} & (5)\end{matrix}$

wherein γ is the clamping length ratio of the bolt, namely the ratio ofthe length of the bolt under tension to the total length; E is theYoung's modulus; a is the acoustic elastic coefficient of the transversewave; β is the acoustic elastic coefficient of the longitudinal waves;C_(S0) and C_(l0) are transverse and longitudinal wave velocities in theabsence of tension; TOF_(S) is the fight time of bolt transverse wave;TOF_(l) is the fight time of bolt longitudinal wave. For the bolt withcalibrated material parameters, the tensile stress applied to the boltcan be calculated as long as TOF_(S) and TOF_(l) can be accuratelymeasured. The transducer used by the invention can simultaneously excitelongitudinal waves and transverse waves on the inspection surface end ofthe bolt. FIG. 6 shows that longitudinal wave (LL) and transverse wave(SS) signals are simultaneously excited on the tested surface end of abolt with 42 mm nominal diameter by using the electromagnetic ultrasonicdouble-wave transducer of the invention. Thus, TOF_(S) and TOF_(l)values can be simultaneously and accurately measured. FIG. 7 is theexperimental raw data of TOF_(S) and TOF_(l) ratio versus tensile stressapplied to the 42 mm-nominal-diameter bolt in FIG. 6. during calibrationby a hydraulic bolt tensile machine. As can be seen from FIG. 7, thecorrespondence between the two is a relatively smooth monotonousfunction in one-to-one correspondence, and the corresponding bolttensile stress error range is relatively small. Professional dataprocessing methods can also be applied to process the one-to-onemonotone function shown in the FIG. 7, so as to obtain higher inspectionprecision for the bolt tensile stress.

For instance, Young's modulus and the Poisson's ratio of isotropicmaterials were measured by using the electromagnetic ultrasonicdouble-wave transducer of embodiment 2.

After selecting the same sample and measurement parameters as inembodiment 1, The FIG. 8 in embodiment 2 corresponds to FIG. 5 ofembodiment 1. In FIG. 8, the amplitude of the longitudinal wavegenerated simultaneously with the transverse wave on the surface of thetesting sample is about one third of that of the embodiment 1, but thefinal detection results of the Young's modulus and the Poisson's ratioare not much different from that of the embodiment 1. In addition, theelectromagnetic ultrasonic double-wave transducer of embodiment 2 isdirectional, and is very advantageous for detecting the sound velocityof transverse waves and the longitudinal waves in each direction of amaterial having a regular texture, such as a cold-rolled steel sheet oran aluminum sheet.

The above embodiments are provided only for illustrating the technicalconcepts and features of the invention, and the purpose of the inventionis to provide those skilled in the art with the understanding of theinvention and to implement the invention, and not to limit the scope ofthe invention. All equivalent changes and modifications made accordingto the spirit of the invention should all fall within the protectionscope of the invention.

1. An electromagnetic ultrasonic double wave transducer, comprising ashell (1), and a permanent magnet assembly, a coil (4), a shieldinglayer (5), and a wire (6) which are provided in the shell (1); saidpermanent magnet assembly comprises a first permanent magnet (2) and asecond permanent magnet (3) sleeved on the first permanent magnet (2);the magnetizing directions of the first permanent magnet (2) and thesecond permanent magnet (3) are perpendicular to the bottom of the shell(1), and the magnetic field directions of the first permanent magnet (2)and the second permanent magnet (3) are opposite; a non-conductingnon-magnetic bushing material (9) is provided between the firstpermanent magnet (2) and the second permanent magnet (3), and upper endfaces of the first permanent magnet (2) and the second permanent magnet(3) realize magnetic circuit closing by means of a magnetic circuitclosing element (8); said coil (4) is fixed on the bottom of said shell(1) and is located below said first permanent magnet (2); said shieldinglayer (5) is provided between the lower end of said first permanentmagnet (2) and said coil (4) and below said second permanent magnet (3);one end of said wire (6) is connected to said coil (4), and the otherend is connected to the power supply and signal plug (7).
 2. Theelectromagnetic ultrasonic double-wave transducer of claim 1 whereinsaid first permanent magnet (2) is cylindrical while said secondpermanent magnet (3) is annular.
 3. The electromagnetic ultrasonicdouble-wave transducer of claim 2 wherein the inner diameter of saidsecond permanent magnet (3) is 1-15 mm larger than the outer diameter ofsaid first permanent magnet (2).
 4. The electromagnetic ultrasonicdouble-wave transducer of claim 2 wherein the lower end faces of saidfirst permanent magnet (2) and said second permanent magnet (3) have aheight difference of −3 mm to 3 mm.
 5. The electromagnetic ultrasonicdouble-wave transducer of claim 2 wherein said coil (4) is helical, andthe outer diameter thereof is larger than or equal to the outer diameterof said first permanent magnet (2) and smaller than the inner diameterof said second permanent magnet (3).
 6. An electromagnetic ultrasonicdouble-wave transducer, comprising a shell (1), and a permanent magnetassembly, a coil (4), a shielding layer (5), and a wire (6) which areprovided in said shell (1); said coil (4) is fixed on the bottom of saidshell (1) and is located below said permanent magnet assembly; saidshielding layer (5) is arranged between said permanent magnet assemblyand said coil (4); one end of said wire (6) is connected to said coil(4) while the other end thereof is connected to the power supply andsignal plug (7); said permanent magnet assembly comprises a thirdpermanent magnet (12) and a fourth permanent magnet (13) wherein thefourth permanent magnet (13) are arranged side by side with said thirdpermanent magnet (12) and located on two sides of the width direction ofsaid third permanent magnet (12), and said fourth permanent magnet (13)and said third permanent magnet (12) are arranged at intervals and saidintervals are made of non-conducting non-magnetic bushing material (9);the upper end faces of said third permanent magnet (12) and said fourthpermanent magnet (13) realize magnetic circuit closing by means of amagnetic circuit closing element (8).
 7. The electromagnetic ultrasonicdouble-wave transducer of claim 6 wherein the cross sections of everymagnet of said third permanent magnet (12) and said fourth permanentmagnet (13) is rectangular.
 8. The electromagnetic ultrasonicdouble-wave transducer of claim 6 wherein said coil (4) is butterflyshaped.
 9. The electromagnetic ultrasonic double-wave transducer ofclaim 1 or claim 6 wherein the non-conductive material (10) is filledbetween said coil (4) and said shielding layer (5), and thenon-conducting non-magnetic material (11) is filled between saidpermanent magnet assembly and said shell (1).
 10. The electromagneticultrasonic double-wave transducer of claim 1 or claim 6 wherein saidshell (1) includes a shell body (1-1) and a wear plate (1-2) disposed atthe lower end of said shell body (1-1).